The present invention relates to the field of personal identification and verification, and, more particularly, to the field of fingerprint sensing and processing.
Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A typical electronic fingerprint sensor is based upon illuminating the finger surface using visible light, infrared light, or ultrasonic radiation. The reflected energy is captured with some form of camera, for example, and the resulting image is framed, digitized and stored as a static digital image. For example, U.S. Pat. No. 4,210,899 to Swonger et al. discloses an optical scanning fingerprint reader cooperating with a central processing station for a secure access application, such as admitting a person to a location or providing access to a computer terminal. U.S. Pat. No. 4,525,859 to Bowles similarly discloses a video camera for capturing a fingerprint image and uses the minutiae of the fingerprints, that is, the branches and endings of the fingerprint ridges, to determine a match with a database of reference fingerprints.
Unfortunately, optical sensing may be affected by stained fingers or an optical sensor may be deceived by presentation of a photograph or printed image of a fingerprint rather than a true live fingerprint. In addition, optical schemes may require relatively large spacings between the finger contact surface and associated imaging components. Moreover, such sensors typically require precise alignment and complex scanning of optical beams. Accordingly, optical sensors may thus be bulky and be susceptible to shock, vibration and surface contamination. Accordingly, an optical fingerprint sensor may be unreliable in service in addition to being bulky and relatively expensive due to optics and moving parts.
U.S. Pat. No. 4,353,056 to Tsikos discloses another approach to sensing a live fingerprint. In particular, the patent discloses an array of extremely small capacitors located in a plane parallel to the sensing surface of the device. When a finger touches the sensing surface and deforms the surface, a voltage distribution in a series connection of the capacitors may change. The voltages on each of the capacitors is determined by multiplexor techniques. Unfortunately, the resilient materials required for the sensor may suffer from long term reliability problems. In addition, multiplexing techniques for driving and scanning each of the individual capacitors may be relatively slow and cumbersome. Moreover, noise and stray capacitances may adversely affect the plurality of relatively small and closely spaced capacitors.
Significant advances have been made in the area of integrated circuit fingerprint sensors, as disclosed, for example, in U.S. Pat. Nos. 5,828,773 and 5,862,248, both assigned to the assignee of the present invention. The disclosed sensors are based upon generating an electric field which can sense the ridges of a fingerprint despite contamination, skin surface damage, and other factors. The sensor is relatively compact and rugged. The sensing die may be mounted on a leadframe so that the conductive pins extend outwardly from side edges of the package for connection to a circuit board.
As disclosed in U.S. Pat. No. 5,862,248 to Salatino et al., an electrically conductive ring may be formed surrounding an opening in the encapsulating package. The integrated circuit die is exposed through the opening. The conductive ring may be used to drive the finger of the user to produce the fingerprint image from a plurality of sensing electrodes on the surface of the integrated circuit. Electrical contact between the conductive ring and the integrated circuit may be established by positioning the ring on an insulating layer on the die and forming one or more conductor filled vias through the insulating layer.
U.S. Pat. No. 5,940,526 to Setlak et al. discloses additional advances in the area of electric field fingerprint sensors. In particular, two electrically conductive rings are provided on the exterior upper surface of the housing. One ring may be used to discharge accumulated electrical charge from the finger of the user. The other electrode can be used to sense finger contact to thereby wake-up the device and supply power thereto. Connections from the integrated circuit die to the external rings may be made by conductor filled vias extending through the housing.
Unfortunately, manufacturing may be somewhat awkward to establish the connection to the external electrodes carrier by the housing for contact with the finger of the user. Conductor filled vias through the housing may be difficult to accurately form and ensure reliable contact.
In view of the foregoing background, it is therefore an object of the present invention to provide a fingerprint sensor and related methods to facilitate ease of manufacture and ensure reliable connection to the one or more external electrodes carried by the housing of the sensor.
This and other objects, features and advantages in accordance with the present invention are provided by a fingerprint sensor comprising a housing, a fingerprint sensing integrated circuit in the housing, and a leadframe comprising at least one first conductive pin extending upwardly to the upper surface and at least one second conductive pin extending outwardly from the housing. The sensor also includes at least one conductive layer on the upper surface of the housing and this is connected to the at least one first conductive pin. The at least one first conductive pin preferably terminates flush with the upper surface of the housing. In other words, one or more upwardly bent leadframe pins readily establish connection to the respective one or more external electrodes.
The integrated circuit may include a finger drive circuit and the at least one conductive layer is connected to the finger drive circuit by the at least one first conductive pin. The circuit may include an electrostatic discharge circuit, and the at least one first conductive pin connects to the electrostatic discharge circuit. The integrated circuit may also include a wake-up circuit and wherein the at least one conductive layer is connected to this wake-up circuit by the at least one first conductive pin.
The housing preferably has an opening therein aligned with the integrated circuit for permitting finger contact with the sensing portion of the integrated circuit. The integrated circuit may include a plurality of electric field sensing electrodes. In addition, a respective shield electrode may surround each of the electric field sensing electrodes. The leadframe preferably comprises metal, and the housing may preferably be provided by an integrally molded body of encapsulating material.
A method aspect of the invention is for making an integrated circuit package of a type including a leadframe, an integrated circuit connected to the leadframe, a housing surrounding the leadframe and the integrated circuit, and at least one electrically conductive layer on a predetermined surface of the housing. The leadframe preferably comprises a plurality of conductive pins. The method preferably comprises: forming at least one first conductive pin of the leadframe to extend to a predetermined surface of the housing; forming at least one second conductive pin of the leadframe to extend outwardly from the housing; and forming at least one conductive layer on the predetermined surface of the housing and connected to the at least one first conductive pin.
Of course, the integrated circuit may preferably comprise a fingerprint sensing integrated circuit. In addition, the predetermined surface may be an upper surface which has an opening therein to permit finger contact with the fingerprint sensing integrated circuit.